The present invention relates to a liquid-crystal display device which is suitably used particularly in a method of selecting plural scanning electrodes in the form of lines at the same time and driving them, and to a method of driving the same.
Generally, since liquid-crystal display devices have features, such as small size and low profile, low power consumption, and flat-panel display, they are widely used in display portions of wristwatches, portable game machines, notebook-type personal computers, liquid-crystal televisions, car navigation devices, and other electronic devices.
As methods of driving a liquid-crystal display panel, there are a driving method of selecting scanning electrodes one at a time and driving them, and an MLS (multi-line selection) driving method (refer to International Application Publication No. WO93/18501) in which all scanning electrodes are grouped in advance and a scanning signal is simultaneously output to plural adjacent scanning electrodes belonging to the same group in a predetermined period. The MLS driving method has an advantage in that power consumption can be reduced.
An example of a conventional liquid-crystal display device using an MLS driving method will now be described with reference to FIGS. 11 to 13. As shown in FIG. 11, a conventional liquid-crystal display device 100 has a liquid-crystal display panel 101. As shown in FIG. 12, the liquid-crystal display panel 101 has a substrate having plural scanning electrodes (common electrodes) Y (Y1, Y2, . . . Ym) in the form of lines, a substrate having plural signal electrodes (segment electrodes) X (X1, X2, . . . Xn) in the form of lines, and a liquid-crystal layer (not shown) interposed between the two substrates. In order to drive the liquid-crystal display panel 101, a liquid-crystal driving circuit 102 supplies, to each scanning electrode Y, a scanning signal which can differ according to each scanning electrode and supplies, to each signal electrode X, a data signal which can differ according to each signal electrode. A liquid-crystal driving voltage generation circuit 103, which is connected to an input end of the liquid-crystal driving circuit 102, generates a liquid-crystal driving voltage. A driving control circuit 104 is connected to the input ends of the liquid-crystal driving circuit 102 and the liquid-crystal driving voltage generation circuit 103. When the driving control circuit 104 receives display data and control data, the driving control circuit 104 generates a display signal and supplies it to the liquid-crystal driving circuit 102 and the liquid-crystal driving voltage generation circuit 103.
The liquid-crystal driving circuit 102 comprises a driving circuit 105 on the scanning side which generates a scanning signal which is output to a scanning electrode Y of the liquid-crystal display panel 101 and a driving circuit 106 on the signal side which generates a data signal which is output to a signal electrode X thereof when the liquid-crystal driving voltage and the display signal are received.
Next, the driving operation of the liquid-crystal display device 100 is described with reference to FIGS. 12 and 13. In this technique, the scanning electrodes Y are grouped in advance so that plural (3 in the example of the figures) adjacent scanning electrodes belong to the same group. The driving circuit 105 on the scanning side drives three scanning electrodes Y belonging to the same group at the same time. That is, the driving circuit 105 on the scanning side generates a scanning signal corresponding to each of the three scanning electrodes Y in a predetermined horizontal scanning period T. Then, another group is driven at the same time, and the process proceeds to the driving of another group in sequence. On the other hand, the driving circuit 106 on the signal side generates a data signal corresponding to each one of the signal electrodes X1, X2, . . . Xn.
Specifically, as shown in part (a) of FIG. 13, the three scanning electrodes Y1, Y2, and Y3 of the first group are selected in the first horizontal scanning period T, scanning signals are applied to these scanning electrodes Y1, Y2, and Y3, and at the same time, data signals are applied to the signal electrodes X. As shown in FIG. 13, the scanning signal and the data signal can change in an interval of a selection period xcex94t even within the same horizontal scanning period T. In the next horizontal scanning period T, as shown in part (b) of FIG. 13, the scanning electrodes Y4, Y5, and Y6 of the next group are selected, and scanning signals having a waveform similar to that supplied to the scanning electrodes Y1, Y2, and Y3 are applied to those electrodes. The application of the data signals to the signal electrodes X is performed continuously from the previous horizontal scanning period T, and the waveform is different from the previous one. In this manner, the process proceeds to the driving of the next group, and when the driving of the final group is terminated, the process returns to the driving of the first group. The period of time required for the driving of all the scanning electrode groups to be completed once, that is, the period of time required to scan one display area of the liquid-crystal display panel 101 once, is called xe2x80x9cone framexe2x80x9d (as indicated by F in FIG. 13).
Since the voltage level of the scanning signal exists at two levels, +V2 and xe2x88x92V2, if the number of scanning electrodes Y belonging to one group (the number of scanning electrodes which are selected at one time) is denoted as h, the number of pulse patterns which can be realized by one group in one selection period xcex94t is 2h. That is, for example, as shown in FIG. 13, in a case where three scanning electrodes Y are selected at the same time, the number of pulse patterns which can be realized by one group in one selection period xcex94t is 23=8. In the first selection period xcex94t in the first horizontal scanning period T, the scanning electrode Y1 is off (voltage=xe2x88x92V2), the scanning electrode Y2 is off, and the scanning electrode Y3 is off. In the next selection period xcex94t, the scanning electrode Y1 is off, the scanning electrode Y2 is off, and the scanning electrode Y3 is on (voltage=+V2), and in sequence, a different pulse pattern is used in each selection period xcex94t.
The data signal applied to each signal electrode X is determined by the on/off of each of the pixels (3 pixels in the case of 3-line simultaneous driving) which are objects for display at the same time on that signal electrode, and the voltage level of the scanning signal applied to the scanning electrode Y. For example, in this conventional technique, during the period in which the voltage of a pulse of a scanning signal applied to the scanning electrodes Y1, Y2, and Y3 which are selected at the same time is positive, the pixel display is assumed to be on; during the period in which the voltage of the pulse is negative, the pixel display is assumed to be off; and the on/off of the display data is compared with the voltage level of the scanning signal at each selection period xcex94t, so that the data signal is set according to the number of mismatches.
Specifically, in the waveforms of the scanning signals sent to the scanning electrodes Y1, Y2, and Y3 in part (a) of FIG. 13, during the period in which a voltage of +V2 is applied, the pixel display is assumed to be on; during the period in which a voltage of xe2x88x92V2 is applied, the pixel display is assumed to be off; a pixel in FIG. 12 whose display is indicated as a black circle mark is assumed to be on, and a pixel whose display is indicated as a white circle mark is assumed to be off. The displays of the pixels at which the signal electrode X1 intersects the scanning electrodes Y1, Y2, and Y3 in FIG. 12 are on, on, and off, in that order. It is assumed that data signals for obtaining such pixel displays are supplied. In contrast, the voltages applied to the scanning electrodes Y1, Y2, and Y3 in the first selection period xcex94t indicate off, off, and off, respectively. Then, when both of the voltages of the display data and of the scanning signals are compared with each other in sequence, the number of mismatches is 2. Therefore, in the first selection period xcex94t, a voltage V1 is applied to the signal electrode X1, as shown in part (c) of FIG. 13. In the technique shown in FIG. 13, when the number of mismatches is 0, a pulse voltage of xe2x88x92V2 is applied to the signal electrode X; when the number of mismatches is 1, a pulse voltage of xe2x88x92V1 is applied thereto; when the number of mismatches is 2, a pulse voltage of V1 is applied thereto; and when the number of mismatches is 3, a pulse voltage of V2 is applied thereto. The voltage ratio of V1 and V2 is set so as to satisfy V1:V2=1:2.
In the next selection period xcex94t, the voltages applied to the scanning electrodes Y1, Y2, and Y3 indicate off, off, and on, respectively. When these are compared with the on, on, and off displays of the pixels in sequence, all the voltage levels of the scanning signals do not match, and the number of mismatches is 3. Therefore, a pulse voltage V2 is applied to the signal electrode X1 in this selection period xcex94t. In a similar manner, in the third selection period xcex94t, V1 is applied to the signal electrode X1 at the third selection period xcex94t, and xe2x88x92V1 is applied thereto in the fourth selection period xcex94t. Hereafter, voltages are applied in the sequence of xe2x88x92V2, +V1, xe2x88x92V1, and xe2x88x92V1.
Furthermore, in the next horizontal scanning period T, the scanning electrodes Y4 to Y6 of the next group are selected. When voltages having waveforms shown in part (b) of FIG. 13 are added to these scanning electrodes Y4 to Y6, a data signal of a voltage level corresponding to the mismatch between the on/off display of the pixels at which the scanning electrodes Y4 to Y6 intersect the signal electrodes and the on/off of the voltage levels of the scanning signals applied to the scanning electrodes Y4 to Y6 is applied to the signal electrode X1, as shown in part (c) of FIG. 13. Part (d) of FIG. 13 shows a waveform indicating a voltage applied to the pixel at which the scanning electrode Y1 intersects the signal electrode X1, that is, a combined waveform of the scanning signal applied to the scanning electrode Y1 and the data signal applied to the signal electrode X1.
As described above, in the MLS driving method for selecting plural scanning electrodes at the same time in sequence and driving them, satisfactory contrast can be obtained, and furthermore, the driving voltage can be reduced.
In the liquid-crystal display device 100 using the MLS driving method according to the above-described conventional art, the on/off of display pixels is controlled by a combination of waveforms of a scanning signal supplied to the scanning electrode Y and a data signal supplied to the signal electrode X. For this reason, since it is necessary to set waveforms to be supplied to both of the electrodes in advance, it is difficult to diversify display modes irrespective of how the scanning electrodes are grouped.
For example, regarding the size of font to be used, in the case of 3-line MLS for selecting three scanning electrodes at the same time, grouping into a multiple of 3, such as 3 pixels, 6 pixels, or 9 pixels, in the vertical direction is easy. However, selection of other numbers of pixels causes signal control to be complex.
Furthermore, partial driving in which the screen of the liquid-crystal display panel 101 is divided into display areas and non-display areas is often performed to reduce power consumption. Here, in the conventional MLS driving method, since plural scanning electrodes belonging to the same group are always driven simultaneously, the width of the display area is completely limited by grouping. For example, if three scanning electrodes are driven at the same time, the display area can have only a width corresponding to lines of a multiple of 3. This applies similarly to multi-row display, in which plural display areas are provided, in partial driving.
The present invention provides a liquid-crystal display device employing an MLS driving method capable of realizing various displays, and a method of driving the same.
According to one aspect of the present invention, the liquid-crystal display device comprises:
a liquid-crystal display panel having a substrate having plural scanning electrodes in the form of lines, a substrate having plural signal electrodes in the form of lines, and a liquid-crystal layer interposed between the substrates;
a scanning signal generation section which is capable of generating h (h is an integer of 2 or more) types of scanning signals, which supplies the scanning signal to each of the h scanning electrodes at the same time in one period, and which supplies the scanning signal to each of the h scanning electrodes at the same time in another period;
a data signal supply section for supplying a data signal to each of the signal electrodes;
a signal selection section for selectively controlling each of the scanning electrodes so as to be capable of producing a display or so as to be incapable of producing a display; and
a control section for controlling the scanning signal generation section in such a way that the scanning signal generation section supplies the scanning signal to the scanning electrode which is controlled by the signal selection section so as to be capable of producing a display.
The signal selection section may comprise plural registers for storing data for causing each of the scanning electrodes to be capable of producing a display or to be incapable of producing a display.
A scroll control section for controlling the signal selection section may be provided so that the electrode which is capable of producing a display and the electrode which is incapable of producing a display are made to shift as time elapses.
According to one aspect of the present invention, the method of driving a liquid-crystal display device comprising a liquid-crystal display panel having a substrate having plural scanning electrodes in the form of lines, a substrate having plural signal electrodes in the form of lines, and a liquid-crystal layer interposed between the substrates, the method comprising the steps of:
generating h (h is an integer of 2 or more) types of scanning signals, supplying the scanning signal to each of the h scanning electrodes at the same time in one period, and supplying the scanning signal to each of the h scanning electrodes at the same time in another period; supplying a data signal to each of the signal electrodes;
selectively controlling each of the scanning electrodes so as to be capable of producing a display or so as to be incapable of producing a display; and
controlling the scanning signal generation section in such a way that the scanning signal generation section supplies the scanning signal to the scanning electrode which is controlled by the signal selection section so as to be capable of producing a display.